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Fractional-frequency-modulation PLL synthesizer that suppresses spurious signals

a phaselocked loop and frequency modulation technology, applied in the direction of pulse generators, pulse techniques, electric pulse generator circuits, etc., can solve the problems of inability to eliminate the variation between gate elements, create problems, and vary the amount of spurious signal suppression

Inactive Publication Date: 2003-12-04
RENESAS ELECTRONICS CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

This in effect leads to variation in the amount of spurious signal suppression.
Especially, in the case of application in wireless equipments like cellular / mobile phones, the spurious signal works as an interference and creates problems.
However, even in such cases, it is not possible to eliminate variation between gate elements resulting from reasons like manufacturing variation etc.
Moreover, when the amount of variation is substantially large, the degree of spurious signal suppression gets deteriorated and poses operational problem that needs to be solved.

Method used

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  • Fractional-frequency-modulation PLL synthesizer that suppresses spurious signals
  • Fractional-frequency-modulation PLL synthesizer that suppresses spurious signals
  • Fractional-frequency-modulation PLL synthesizer that suppresses spurious signals

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Embodiment Construction

[0031] FIG. 8 shows the basic configuration of the fractional-frequency-mo-dulation-type PLL synthesizer according to the present invention. In this diagram, reference numeral 101 represents reference oscillator, 102 reference frequency divider, 103 phase comparator, 104a charge pump circuit, 105 loop filter, 106 voltage control oscillator, 107 variable frequency divider, 108 frequency change-over circuit, 109 shift resistor, 110 adder, 111 accumulator and 113a charge pump bias circuit.

[0032] The operation of the fractional-frequency-modulation-type PLL synthesizer is explained with the help of FIG. 8 and FIG. 4. As shown in FIG. 8, the reference oscillator 101 generates a signal Fosc and inputs the generated signal into the reference frequency divider 102. The reference frequency divider 102 divides the signal Fosc to obtain a reference frequency signal Fref. The reference frequency divider 102 feeds the reference frequency signal Fref to the phase comparator 103. The phase compara...

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Abstract

The phase comparator in the PLL synthesizer has first and second transmission gates of identical shape connected to the front and back row of 2N-1 gate delay elements. Third and fourth transmission gates are permanently set to ON setting. The first transmission gate and the NAND gates operate as a gate delay element when the COUNT signal is of low logical level and operate as a ring oscillator when the COUNT signal is of high logical level.

Description

[0001] 1) Field of the Invention[0002] The present invention is related to a fractional-frequency-modulati-on-type phase-locked-loop (PLL) synthesizer that suppresses spurious elements.[0003] 2) Description of the Related Art[0004] Fractional-frequency-modulation-type PLL synthesizer allows fractional (sub-decimal point) frequency modulation settings as an average frequency modulation by periodically changing over frequency modulation of variable frequency divider. The fractional-frequency-modula-tion-type PLL synthesizer has two prominent merits as explained below:[0005] (1) It is possible to reduce frequency modulation of variable frequency divider owing to higher reference frequency (phase comparator frequency) setting than that of channel resolution. This leads to increase in PLL loop gain enabling reduction in frequency change-over time.[0006] (2) It is possible to reduce in-phase noise due to reduction of frequency modulation of the variable frequency divider.[0007] FIG. 3 sho...

Claims

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Application Information

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IPC IPC(8): H03K5/26H03C3/09H03D13/00H03L7/089H03L7/197
CPCH03C3/0925H03L7/1976H03L7/0898H03D13/004
Inventor KAWAHARA, TADASHI
Owner RENESAS ELECTRONICS CORP